Taking Supreme Leader Snoke from a vague hologram to a physical presence was one of the biggest challenges for the visual effects team on Star Wars: The Last Jedi, and the process was a complex push and pull between the director, the effects artists, and Andy Serkis, who portrayed Snoke in motion capture and voice.
Info on that process comes from an in-depth interview between Deadline and Oscar-nominated VFX supervisors Ben Morris and Mike Mulholland, who both also worked on The Force Awakens. In it, they describe a multi-stage process that transformed Snoke from a silhouette to a person, monstrous, thin, and imposing, as Morris explained:
Rian got a sculpt done by the creature team, which completely transformed the look of Snoke away from the almost gelatinous zombie look that was in The Force Awakens, and stamped him into the real world. We had that maquette on set, and we also made sure that we had an older actor who we could shoot on every time we had a shot. So we would have Andy Serkis in his performance capture outfit. He'd have a head-mounted camera system on — we actually had four cameras, two stereo pairs watching his face. We were capturing his body movements, and we had two or three witness cameras in addition, so we covered all of that. We also had this reference maquette, and then an older age person and a younger, very tall actor, who wore the incredible golden gown — which, again, is entirely CG in the film.
With all of that reference, Rian went into editorial and started cutting together the sequences. Andy's got this wonderful resonant voice, and we started to watch the whole thing come together without any CG Snoke in there. It was working beautifully well. As Mike and the team started to put together CG Snoke per the sculpt that had been approved, we suddenly realised that he was a far more imposing character. Andy's voice gave a sense of a larger chest cavity. His throat carried far more timbre. When you look to the CG model that we were building that matched the sculpt, he just looked too flimsy and frail. We had to put the brakes on and say, "We're going to have to change this."
We did a number of broader things — we made him over eight feet tall, rather than seven feet tall. We expanded his chest. We restructured all the anatomy of his throat, and we took some scoliotic curvature out of his spine that was a feature of the original sculpt. We also restructured his jawline, to give him more of an imposing face.
Serkis, it seems, played a huge role in shaping the appearance of the character by virtue of his performance alone. The Snoke that appeared as a result of this back and forth is a stranger, more threatening sort of villain. He has a frailty about him, but he also exudes a fascinating menace, his presence reverberating across the entire throne room.
After rebuilding the image of Snoke to communicate that presence, the team transferred Serkis' performance to CG and built it into Snoke, said Mulholland:
Doing those modifications tied our Snoke to Andy's voice, so it was no longer clashing. The key was to try and capture the essence of the actor and make sure that you're able to transmit that into the CG character. Our work was to first of all make a CG version of Andy, who didn't look like Snoke at that point. It was Andy talking, and you move that performance onto Snoke. Once we'd done the technical side of the transfer, the animation team would go in and work to eek out all the subtleties and intonations, and the expressions were even slightly modified so they worked better on our Snoke character. It was a painstaking process to go beat by beat and make sure that it was the performance that Rian remembered from set, and that was what Rian held us to.
That's a complicated process for what ends up being a relatively small part. But it's worth it: Snoke is an unlikely highlight of The Last Jedi.
Also, you should check out the rest of this interview at the link below. It's got a lot of interesting stuff in it.